1. Technical Field
One or more embodiments of the present invention generally relate to a metal wiring layer, and a method of fabricating the same. More particularly, one or more embodiments of the present invention relate to a buried-type metal wiring layer, and a method of fabricating the same.
2. Description of the Related Art
As a flat panel display, a liquid crystal display (LCD) includes a lower substrate on which a plurality of gate lines, a plurality of data lines, a plurality of pixel electrodes and a plurality of thin-film transistors (TFTs) are formed, an upper substrate on which a common electrode is formed, and a liquid crystal layer which is interposed between the lower substrate and the upper substrate. An LCD generates an electric field in a liquid crystal layer by applying a voltage to a plurality of pixel electrodes and a common electrode, and thus displays an image by determining the alignment of liquid crystal molecules in the liquid crystal layer and by controlling the polarization of incident light.
In order to realize a large-scale LCD having high resolution, it is necessary to reduce the resistance of metal wiring. To accomplish this, metal wiring may be formed of a low-resistance material such as copper (Cu) or silver (Ag). In order to further reduce the resistance of metal wiring, the width or the thickness of metal wiring must be increased.
However, as the width of metal wiring increases, the area of pixel regions decreases, and thus, the transmittance of a liquid crystal layer deteriorates. Furthermore, as the thickness of metal wiring increases, a step difference between a substrate and the metal wiring may increase. For example, if a gate line including a gate electrode is formed to a thickness of 4000-5000 Å, a huge step difference may be generated between the substrate and the gate line. The step difference between the substrate and the gate line may further increase by laying source and drain electrodes over the gate electrode. When a lower substrate has such a huge step difference, a liquid crystal layer may not be properly filled with liquid crystal molecules. As a result, the transmittance of the liquid crystal layer may become irregular due to an irregular alignment of liquid crystal molecules in the liquid crystal layer, and the quality of display may deteriorate.
In order to address this problem, methods of forming a buried-type metal wiring layer have been suggested, in which a trench is formed on a substrate and a metal wiring layer is formed in the trench through electroplating. These methods, however, may result in various defects such as an edge build-up phenomenon, in which a metal layer is excessively grown along the edges of a trench and thus the metal layer becomes thicker near the edges than at other regions in the trench.